Motors or power engines are used as a power driving source in industrial apparatuses, household electrical appliances, automotive vehicles, railways, and the like. In such power machines, an output torque and the number of revolutions of the motor or the power engine are reduced by a mechanical gear and are converted to a required torque and number of revolutions when using in many cases. However, when a high-speed electric machine is used together with a mechanical gear box, a high system-torque density may be realized. However, there arise necessities of lubrication and cooling. In addition, reliability is also an important problem. Magnetic gear mechanisms studied by aiming the problems described above are disclosed also in Non Patent Literature 1 and in Non Patent Literature 2. This magnetic gear mechanism causes less abrasion and loss due to heat generation in comparison with mechanical gear mechanisms, and is capable of transmitting a relatively high torque.